Cathodic electrocoating composition containing a morpholine dione crosslinking agent

ABSTRACT

An improved aqueous cathodic electrocoating composition having a binder of an epoxy-amine adduct and a crosslinking agent; wherein the improvement is the use of a crosslinking agent having at least one, preferably a plurality of morpholine dione groups per molecule. Electrodeposited finishes are formed that have reduced volatile emissions and film weight loss when heated to cure.

BACKGROUND OF THE INVENTION

This invention is directed to a cathodic electrocoating composition andin particular to a cathodic electrocoating composition containing amorpholine dione crosslinking agent which significantly reduces volatileemissions and bake-off loss that occur from the coating film duringcuring.

The coating of electrically conductive substrates by anelectrodeposition process, also called an electrocoating process, is awell known and important industrial process. Electrodeposition ofprimers on metal automotive substrates is widely used in the automotiveindustry. In this process, a conductive article, such as an autobody oran auto part, is immersed in a bath of a coating composition of anaqueous emulsion of film forming polymer and the article acts as anelectrode in the electrodeposition process. An electric current ispassed between the article and a counter-electrode in electrical contactwith the coating composition until a coating of a desired thickness isdeposited on the article. In a cathodic electrocoating process, thearticle to be coated is the cathode and the counter-electrode is theanode.

Film forming resin compositions used in the bath of a typical cathodicelectrodeposition process also are well known in the art. These resinstypically are made from polyepoxide resins which have been chainextended and then an adduct is formed to include amine groups in theresin. Amine groups typically are introduced through a reaction of theresin with an amine compound. These resins are blended with acrosslinking agent, usually a polyisocyanate, and then neutralized withan acid to form a water emulsion which is usually referred to as aprincipal emulsion.

The principal emulsion is combined with a pigment paste, coalescentsolvents, water, and other additives such as a catalyst to form theelectrocoating bath. The electrocoating bath is placed in an insulatedtank containing the anode. The article to be coated is the cathode andis passed through the tank containing the electrodeposition bath. Thethickness of the coating that is deposited on the article beingelectrocoated is a function of the bath characteristics, the electricaloperating characteristics of the tank, the immersion time, and the like.

The resulting coated article is removed from the bath and is rinsed withdeionized water. The coating on the article is cured typically in anoven at sufficient temperature to form a crosslinked finish on thearticle. The presence of the catalyst enhances the crosslinking of thefinish. Cathodic electrocoating compositions, resin compositions,coating baths and cathodic electrodeposition processes are disclosed inJarabek, et al. U.S. Pat. No. 3,922,253 issued Nov. 25, 1975; Wismer, etal. U.S. Pat. No. 4,419,467 issued Dec. 6, 1983; Belanger U.S. Pat. No.4,137,140 issued Jan. 30, 1979 and Wismer, et al. U.S. Pat. No.4,468,307 issued Aug. 25, 1984.

One disadvantage associated with conventional electrocoatingcompositions containing polyisocyanate crosslinking agents is that inorder to prevent premature gelation of the electrocoating composition,the highly reactive isocyanate groups on the curing agent must beblocked, for example, with an alcohol. Blocked polyisocyanates, however,require high temperatures to unblock and begin the curing reaction. Thiscuring mechanism also releases a substantial amount of volatile blockingagents during curing, which generates unwanted film weight losses, alsoknown as bake-off loss, and makes it necessary to purify the exhaust airdischarged from the oven and constitutes an unwanted loss in resinsolids. In addition, the volatile blocking agents released during curecan cause other deleterious effects on various coating properties, e.g.,producing a rough film surface.

U.S. Pat. No. 4,615,779 to McCollum, et al. issued Oct. 7, 1986 suggeststhe use of lower molecular weight alcohol blocking agents to reduceweight loss when the film is heated to cure. Such blocking agents,however, can produce undesirable film defects. U.S. Pat. No. 5,431,791to December, et al. issued Jul. 11, 1995 describes the use of a curingagent having a plurality of cyclic carbonate groups, in place of blockedpolyisocyanates, which still provides desirable urethane crosslinks butis able to avoid bake-off losses and other problems that accompany theuse of blocked polyisocyanate curing agents. Cyclic carbonates, however,are oftentimes difficult to incorporate into the principal emulsion.

Therefore, there is still a need to find new cross-linking agents forcathodic electrocoating compositions that reduce volatile emissions andbake-off losses, while maintaining the desired coating properties.

SUMMARY OF THE INVENTION

The invention is directed to an improved aqueous cathodic electrocoatingcomposition having a film forming binder of an epoxy-amine adduct, acrosslinking agent for the epoxy-amine adduct and an organic orinorganic acid as the neutralizing agent for the epoxy-amine adduct;wherein the improvement is the use of a crosslinking agent having, on anaverage basis, at least two morpholine dione groups per molecule, thatare capable of reacting with the amine groups on the epoxy-amine adduct.An additional crosslinking agent is also preferably used to provide ahighly crosslinked final film network.

The invention is based on the discovery that the crosslinking reactionbetween morpholine dione groups with amine groups occurs at relativelylow temperature and no volatile by-products are released. Thus, it hasnow been found that bake-off loss on cure can be significantly reducedand the problems that accompany the use of blocked polyisocyanate curingagents can be greatly avoided.

Methods for cathodically electrocoating a conductive substrate using anyof the above-described compositions and conductive articles coatedtherewith also form part of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The electrocoating composition of this invention is an aqueouscomposition preferably having a solids content of about 5-50% by weightof a principal emulsion of a cathodic film forming binder, additives,pigment dispersant resins, pigments and the like and usually contains anorganic coalescing solvent.

The film forming binder of the principal emulsion used to form thecathodic electrocoating composition of this invention is an epoxy-amineadduct and a novel morpholine dione group containing crosslinking agent.The epoxy-amine adduct is usually formed from an epoxy resin whichpreferably is chain extended and then reacted with an amine to providean adduct with amine groups that are subsequently neutralized with anacid. The epoxy-amine adduct usually is blended with the crosslinkingresin and then neutralized with an acid and inverted into water to forman aqueous emulsion, which is referred to as the principal emulsion.Other ingredients are then added to the principal emulsion, such aspigment in the form of a pigment paste, coalescent solvents, anticrateragent, flexibilizers, defoamers, wetting agents, and other additives,such as catalyst, to form a commercial electrocoating composition.Typical aqueous cathodic electrocoating compositions are shown inDeBroy, et al. U.S. Pat. No. 5,070,149 issued Dec. 3, 1991 and theaforementioned U.S. Pat. Nos. 3,922,253; 4,419,467; 4,137,140 and4,468,307.

The advantage of the electrocoating composition of this inventionformulated with the novel morpholine dione crosslinking agent is thatthere is reduced volatile emission and reduced bake-off loss, andattendant weight loss, occurring from the film during cure afterelectrodeposition. In addition, the electrocoating composition exhibitslower curing temperature, better edge corrosion resistance and smootherappearance in comparison to electrocoating compositions that onlycontain conventional alcohol-blocked polyisocyanate crosslinking agents.

The epoxy-amine adduct of the novel composition is formed of an epoxyresin which preferably is chain extended and then reacted with an amine.The resulting epoxy-amine adduct has reactive hydroxyl, epoxy and aminegroups.

The epoxy resin used in the epoxy amine adduct is a polyepoxy-hydroxy-ether resin having an epoxy equivalent weight of about150-2,000.

Epoxy equivalent weight is the weight of resin in grams which containone gram equivalent of epoxy.

These epoxy resins can be any epoxy-hydroxy containing polymer having a1,2-epoxy (i.e., terminal) equivalency of two or more per molecule, thatis, a polyepoxide which has on an average basis two or more epoxy groupsper molecule. Preferred are polyglycidyl ethers of cyclic polyols.Particularly preferred are polyglycidyl ethers of polyhydric phenolssuch as bisphenol A. These polyepoxides can be produced byetherification of polyhydric phenols with epihalohydrin or dihalohydrinsuch as epichlorohydrin or dichlorohydrin in the presence of alkali.Examples of polyhydric phenols are 2,2-bis-(4-hydroxyphenyl)ethane,2-methyl-1,1-bis-(4-hydroxyphenyl)propane,2,2-bis-(4-hydroxy-3-tertiarybutylphenyl)propane,1,1-bis-(4-hydroxyphenol)ethane, bis-(2-hydroxynaphthyl)methane,1,5-dihydroxy-3-naphthalene or the like.

Besides polyhydric phenols, other cyclic polyols can be used inpreparing the polyglycidyl ethers of cyclic polyol derivatives. Examplesof other cyclic polyols are alicyclic polyols, particularlycycloaliphatic polyols, such as 1,2-bis(hydroxymethyl)cyclohexane,1,3-bis-(hydroxymethyl)cyclohexane, 1,2-cyclohexane diol,1,4-cyclohexane diol and hydrogenated bisphenol A.

The epoxy resin can be chain extended, for example, with any of theaforementioned polyhydric phenols. Preferred chain extenders arebisphenol A and ethoxylated bisphenol A and preferably a combination ofthese phenols. Also, the polyepoxides can be chain extended with apolyether or a polyester polyol which enhances flow and coalescence.Typical useful chain extenders are polyols such as polycaprolactonediols, such as Tone 200® series available from Union Carbide/DowCorporation, and ethoxylated bisphenol A, such as SYNFAC 8009® availablefrom Milliken Chemical Company.

Examples of polyether polyols and conditions for chain extension aredisclosed in U.S. Pat. No. 4,468,307. Examples of polyester polyols forchain extension are disclosed in Marchetti et al U.S. Pat. No. 4,148,772issued Apr. 10, 1979.

Typical catalysts that are used in the formation of these polyepoxyhydroxy ether resins are tertiary amines such as dimethylbenzylamine andorganometallic complexes such as ethyl or other alkyl triphenylphosphonium iodide.

Ketimines and/or secondary amines and/or primary amines can be used tocap, i.e., react with the epoxy end groups of the resin to form theepoxy amine adduct. Ketimines, which are latent primary amines, areformed by reacting ketones with primary amines. Water formed in thereaction is removed, for example, by azeotropic distillation. Usefulketones include dialkyl, diaryl, and alkylaryl ketones having 3-13carbon atoms. Specific examples of ketones used to form these ketiminesinclude acetone, methyl ethyl ketone, methyl n-butyl ketone, methylisobutyl ketone, methyl isoamyl ketone, methyl aryl ketone, ethylisoamyl ketone, ethyl amyl ketone, acetophenone, and benzophenone.Suitable diamines are ethylenediamine, 1,3-diaminopropane,1,4-diaminobutane, 1,6-diaminohexane, 4,9-dioxododecane and1,12-dodecanediamine and the like. One typically useful ketimine isdiketimine which is the ketimine of diethylene triamine and methylisobutyl ketone.

Typically useful primary and secondary amines that can be used to formthe epoxy-amine adduct are methylamine, ethylamine, propylamine,butylamine, isobutylamine, benzylamine and the like; and dimethylamine,diethylamine, dipropylamine, diisopropylamine, dibutylamine and thelike. Alkanol amines are preferred, such as ethanolamine, propanolamine,and the like; and methylethanolamine, ethylethanolamine,phenylethanolamine, diethanolamine and the like. Other amines that canbe used are set forth in the aforementioned U.S. Pat. No.4,419,467 whichis hereby incorporated by reference.

It has been discovered that amine groups react with the morpholine dionecrosslinking groups employed in this invention.

The cathodic binder of the electrocoating composition contains about20-80% by weight of the forgoing epoxy amine adduct and correspondingly80-20% of the morphoune dione crosslinking agent.

The coating composition of the present invention, as previouslyindicated, includes a novel curing agent that has on an average basis atleast one, preferably at least two, morpholine dione groups permolecule. As will be understood by those skilled in the art, if only onemorpholine dione group is present, the crosslinking agent will containat least one other crosslinkable group, such as but not limited to amelamine or isocyanate group (blocked or unblocked), to enable the filmto cure. During curing, it is believed that the morpholine dione groups,i.e., the crosslinking functionality, react with amine functional groupsin the electrocoat resin to form a crosslinking network during cure. Thereaction between morpholine dione groups with amine functional groupsoccurs at relatively low temperatures and no volatile by-products arereleased, since a ring-opening reaction is involved. Accordingly, thistype of curing mechanism reduces bake-off loss and does not contributeto weight loss when the film is heated to cure. Also, this curingmechanism has been found to be stable to active hydrogens at roomtemperature but reactive with active hydrogen at only slightly elevatedtemperatures, such as between 275° and 325° F. (135°-162.5° C.).

More particularly, the novel morpholine dione compound used in thisinvention is formed of an epoxy resin which is reacted with an amine toprovide an adduct with amine groups that are subsequently reacted withan oxalate to convert the epoxy groups to morpholine dione groups.Accordingly, the resulting compound has reactive morpholine dionegroups.

The epoxy resin used in preparing the morpholine dione compound is apolyepoxy resin having an epoxy equivalent weight of about 150-2,000,and any of the epoxy resins listed above for use in the epoxy-amineadduct may also be used in the morpholine dione crosslinking agent.

As indicated above, these epoxy resins can be any epoxy-hydroxycontaining polymer having a 1,2-epoxy equivalency of two or more permolecule, that is, a polyepoxide which has on an average basis two ormore epoxy groups per molecule. The preferred are polyglycidyl ethers ofcyclic polyols. Particularly preferred are polyglycidyl ethers ofpolyhydric phenols such as bisphenol A. These polyepoxides can beproduced by etherification of polyhydric phenols with epihalohydrin ordihalohydrin such as epichlorohydrin or dichlorohydrin in the presenceof alkali. Examples of polyhydric phenols are2,2-bis-(4-hydroxyphenyl)ethane,2-methyl-1,1-bis-(4-hydroxyphenyl)propane,2,2-bis-(4-hydroxy-3-tertiarybutylphenyl)propane,1,1-bis-(4-hydroxyphenol)ethane, bis-(2-hydroxynaphthyl)methane,1,5-dihydroxy-3-naphthalene or the like.

Besides polyhydric phenols, other cyclic polyols can be used inpreparing the polyglycidyl ethers of cyclic polyol derivatives. Examplesof other cyclic polyols are alicyclic polyols, particularlycycloaliphatic polyols, such as 1,2-bis(hydroxymethyl)cyclohexane,1,3-bis-(hydroxymethyl)cyclohexane, 1,2-cyclohexane diol,1,4-cyclohexane diol and hydrogenated bisphenol A.

Oligomeric or polymeric polyepoxides, such as acrylic polymers oroligomers containing glycidyl methacrylate or epoxy-terminatedpolyglycidyl ethers, can also be used. Monomers commonly used inpreparing acrylic polymers are styrene, methyl methacrylate, butylacrylate, butyl methacrylate, ethyl hexyl methacrylate, glycidylacrylate, and glycidyl methacrylate, and the like. The acrylic polymer,however, should not contain any hydroxy functional monomers, such ashydroxy alkyl acrylates and methacrylates, since the hydroxyl alcoholgroups can interfere with the morpholine dione group formation reaction.Other polyepoxide resins, such as epoxy-novolacs, particularly epoxycresol and epoxy phenol novolacs, can also be used in the presentinvention to form the principal emulsion. Epoxy novolacs are typicallyproduced by reacting a novolac resin, usually formed by the reaction oforthocresol or phenol and formaldehyde, with epichlorohydrin. As withany of the polyepoxides, epoxy-novolacs can be reacted with alkyl amineand dialkyl oxalate to form the morpholine dione crosslinking agent.

The amines which are used in preparing the morpholine dione arepreferably primary amines. The primary amines react with the epoxygroups of the resin to form amino alcohol groups thereon which arecapable of forming a morpholine dione structure. Useful primary aminesinclude any of those listed above used to form the epoxy-amine adduct.Particularly preferred are alkyl amines having 1-15 carbon atoms in thealkyl group. Most preferred are sterically hindered primary amines suchas t-butyl amine. Hindered amines prevent dimerization of the epoxideand favor the desired epoxy ring opening reaction.

The resulting adduct can then be reacted with any conventional oxalateester to ring close and form the crosslinkable morpholine dione groupsthereon. Alcohol formed in the reaction is removed, for example, byazeotropic distillation. Useful oxalates in forming the morpholine dionecompounds include dialkyl oxalates having 1 to 15 carbon atoms in thealkyl groups, of which diethyl oxalate is most preferred.

Preferably the number average molecular weight of the morpholine dionecompound used in this invention is less than about 2,000, morepreferably less than about 1,500, in order to achieve high flowabilityand high film smoothness. A preferred range for the number averagemolecular weight is between 400 and 1,200. All molecular weightsdisclosed herein are determined by gel permeation chromatography using apolystyrene standard. Preferably, these compounds are activated (i.e.,ring-opened) during aminolysis reactions at much lower bakingtemperatures than standard blocked polyisocyanates, preferably between275° and 325° F. (135°-162.5° C.). By comparison, standard blockedpolyisocyanate are baked nowadays at 330° F. (165.5° C.) or above tounblock the isocyanate and begin the curing reaction.

One preferred class of morpholine dione compounds useful as thecrosslinking agent in the present invention is the reaction product ofan aromatic polyepoxy-hydroxy-ether resin, such as a polyglycidyl etherof bisphenol A, with alkyl amine and dialkyl oxalate. Examples of usefulcompounds within this class are represented by the formula:

-   -   where R is independently an alkyl group having 1-10, preferably        2-6 carbon atoms, and n is 0 or a positive integer from 1-4.        Another preferred class of morpholine dione compounds useful in        the present invention is the reaction product of an epoxy        novolac resin, such as epoxy phenol novolac, with alkyl amine        and dialkyl oxalate. Examples of useful compounds within this        class are represented by the formula:    -   where R is independently an alkyl group having 1-8, preferably        2-6 carbon atoms, and n is 0 or a positive integer from 1-4.

The novel morpholine dione compounds used in the coating composition canbe prepared by any of several different approaches. The preferredprocess for preparing morpholine dione compounds from epoxy resins is astepwise process which involves slowly charging the epoxy resin to areaction vessel containing primary amine and keeping the reactiontemperature at −10° C. to 100° C., preferably at 10° C. to 40° C., untilall of the epoxy groups are reacted as indicated by infrared scan.Preferably, the molar ratio of epoxy to amine groups in the abovereaction is in the range of 1:1 to 1:10, more preferably 1:1, althoughthere are many reasons to vary from this range, as will be appreciatedby those skilled in the art. The reaction is preferably carried in thepresence of a polar solvent such as ethanol for reducing viscosity inthe reaction vessel. Excess amine is preferably removed before theaddition of dialkyl oxalate. Then, dialkyl oxalate and appropriatecatalyst, such as 4-dimethylaminopyridine, are charged to the reactionvessel and the reaction vessel is generally maintained at the refluxtemperature until all the epoxy-amino groups are ring closed andconverted to morpholine dione groups as indicated by infrared scan.Preferably, the molar ratio of amine groups to oxalate groups in theabove reaction is in the range of 0.8:1 to 1:0.8, more preferably 1:1.Alcohol formed in this reaction is removed, for example, by azeotropicdistillation.

Typical catalysts that can be used in the formation process are tertiaryamines and most especially 4-dimethylaminopyridine.

Typical solvents that can be used in the formation process are ketonessuch as methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone,aromatic hydrocarbons such as toluene, xylene, alkylene carbonates suchas propylene carbonate, n-methyl pyrrolidone, ethers, esters, acetatesand mixture of any of the above, although polar solvents such as ethanoland the like are generally preferred.

As indicated above, the reaction conditions are preferably chosen sothat 100% of the epoxy groups are reacted and converted to morpholinedione groups, or as close to 100% as can be reasonably achieved, leavingessentially no unreacted epoxy groups in the molecule.

The resulting morpholine dione compounds are used in the present coatingcomposition in an amount varying from about 10-60%, preferably about15-40%, by weight of the total binder in the composition. Mostpreferably, about 20-30% by weight of such a morpholine dione compoundis included in the binder.

Besides the morpholine dione compounds derived from epoxy resins asdescribed above, other morpholine dione compounds can also be used inthe present invention, as will be appreciated by those skilled in theart.

Optionally, the present coating composition may further, and preferablydoes, include an additional crosslinking agent, in conjunction with themorpholine dione crosslinking agent. The additional crosslinking agentmay comprise 0 to 99% by weight of the total crosslinking component usedin the present coating composition. The additional crosslinking agent isused to react with any remaining active hydrogen groups present in theresin system. Examples of additional crosslinking agents include any ofthe conventionally known blocked polyisocyanate crosslinking agents.These are aliphatic, cycloaliphatic and aromatic isocyanates such ashexamethylene diisocyanate, cyclohexamethylene diisocyanate, toluenediisocyanate, methylene diphenyl diisocyanate and the like. Aromaticdiisocyanates such as methylene diphenyl diisocyanate are preferred.These isocyanates are pre-reacted with a blocking agent such as oximes,alcohols, or caprolactams which block the isocyanate functionality. Onepreferred mixture of blocking agents is methanol, ethanol and diethyleneglycol monobutyl ether. Upon heating, the blocking agents separate,thereby providing a reactive isocyanate group and additionalcrosslinking occurs with the epoxy-amine adduct. Isocyanate crosslinkersand blocking agents are well known in the art and also are disclosed inMarchetti et al U.S. Pat. No. 4,419,467 issued Apr. 10, 1979, herebyincorporated by reference. Melamine crosslinking agents could also beused.

The cathodic binder of the epoxy amine adduct and the crosslinkingagent(s) are the principal resinous ingredients in the electrocoatingcomposition and are usually present in amounts of about 30 to 50% byweight of solids of the composition. The basic groups (amine groups) ofthe cathodic binder are partially or totally neutralized with an acid toform a water soluble product. Typical acids used to neutralize theepoxy-amine adduct to form water-dispersible cationic groups are lacticacid, acetic acid, formic acid, sulfamic acid, alkane sulfonic acidssuch as methane sulfonic acids, ethane sulfonic acid, propane sulfonicacid and the like. Alkane sulfonic acids are generally preferred. Thedegree of neutralization depends upon the properties of the binderemployed in each individual case. In general, sufficient acid is addedto provide the resulting electrocoating composition with a pH of about5.5-8.0. To form an electrocoating bath, the solids of theelectrocoating composition are generally reduced with an aqueous mediumto the desired bath solids.

Besides the binder resin ingredients described above, the electrocoatingcomposition usually contains pigment which is incorporated into thecomposition in the form of a pigment paste. The pigment paste isprepared by grinding or dispersing a pigment into a grinding vehiclewith curing catalyst and other optional ingredients such asanticratering agents wetting agents, surfactants, and defoamers. Any ofthe pigment grinding vehicles that are well known in the art can beused. Typically, grinding is done using conventional equipment known inthe art such as an Eiger mill, Dynomill or sand mill. Generally grindingis carried out for about 2 to 3 hours until a minimum of 7 or greaterHegman reading is obtained.

Viscosity of the pigment dispersion before it is ground or milled isimportant. B Brookfield viscosity typically is used as determined inaccordance with ASTM D-2196. While the desired viscosity will vary withthe selected components, viscosity generally will be in the range of8000 centipoise to 1500 centipoise (0.8 Pa.s to 1.5 Pa.s) to achieve afine grind during grinding. Viscosity typically increases duringgrinding and is readily adjusted by modifying the amount of waterpresent.

Pigments which can be used in this invention include titanium dioxide,basic lead silicate, strontium chromate, carbon black, iron oxide, clayand the like. Pigments with high surface areas and oil absorbenciesshould be used judiciously because these can have an undesirable affecton coalescence and flow of the electrodeposited coating.

The pigment to binder weight ratio is also important and should bepreferably less than 5:1, more preferably less than 4:1, and usuallyabout 2 to 4:1. Higher pigment to binder weight ratios have been foundto adversely affect coalescence and flow.

The electrocoating compositions of the invention can contain optionalingredients such as wetting agents, surfactants, defoamers and the like.Examples of surfactants and wetting agents include alkyl imidazolinessuch as those available from Ciba-Geigy Industrial Chemicals as AmineC®, acetylenic alcohols available from Air Products and Chemicals asSurfynol 104®. These optional ingredients, when present, constitute fromabout 0.1 to 20 percent by weight of binder solids of the composition.

Optionally, plasticizers can be used to promote flow. Examples of usefulplasticizers are high boiling water immiscible materials such asethylene or propylene oxide adducts of nonyl phenols or bisphenol A.Plasticizers are usually used at levels of about 0.1 to 15 percent byweight resin solids.

Curing catalysts such as tin are usually present in the composition.Examples are dibutyltin dilaurate and dibutyltin oxide. When used, theyare typically present in amounts of about 0.05 to 2 percent by weighttin based on the weight of total resin solids.

The electrocoating compositions of this invention are dispersed in anaqueous medium. The term “dispersion” as used within the context of thisinvention is believed to be a two-phase translucent or opaque aqueousresinous binder system in which the binder is in the dispersed phase andwater the continuous phase. The average particle size diameter of thebinder phase is about 0.05 to 10 μm, preferably, less than 0.2 μm. Theconcentration of the binder in the aqueous medium in general is notcritical, but ordinarily the major portion of the aqueous dispersion iswater. The aqueous dispersion usually contains from about 3 to 50percent, preferably 5 to 40 percent, by weight binder solids. Aqueousbinder concentrates which are to be further diluted with water whenadded to an electrocoating bath, generally have a range of binder solidsof 10 to 30 percent weight.

Besides water, the aqueous medium of the cathodic electrocoatingcomposition contains a coalescing solvent. Useful coalescing solventsinclude hydrocarbons, alcohols, polyols, and ketones. Preferredcoalescing solvents include monobutyl and monohexyl ethers of ethyleneglycol and phenyl ether of propylene glycol. The amount of coalescingsolvent is not critical but generally is between 0.1 to 15% by weight,preferably 0.5% by weight, based on the total weight of the aqueousmedium.

The electrocoating composition of this invention is used in aconventional cathodic electrocoating process. The electrocoating tankcontains two electrically conductive electrodes: the anode which is partof the electrocoating tank and the cathode which is the substrate thatis to be coated. This substrate may be any electrically conductive(e.g., metal) object, including but not limited to items such as an autobody or auto part or any other OEM or industrially coated part,including but not limited to, yard equipment (e.g., lawn mowers, snowblowers, gardening and power tools, and parts therefore), officefurniture, household appliances, children's toys, and the like. Anadherent film is deposited on the cathode when a sufficient voltage isimpressed between the two electrodes. The voltages that are applied maybe varied depending on the type of coating and on coating thickness andthrow power required and may be as low as 1 volt or as high as severalthousand volts. Typical voltages used are between 50-500 volts. Thecurrent density usually is between 0.5 and 5 amperes per square foot(4.65 and 46.5 amperes per square meter), and decreases duringelectrodeposition indicating that an insulating film is being deposited.The immersion time should be sufficient to obtain a cured coating ofabout 0.5-1.5 mils (10-40 μm), preferably 0.8-1.2 mils (20-30 μm). Avariety of substrates can be electrocoated with the composition of thisinvention, such as steel, phosphatized steel, galvanized steel, copper,aluminum, magnesium, and various plastics coated with an electricallyconductive coating.

After the coating has been electrocoated, it is cured by baking atelevated temperatures such as 135-200° C. for a sufficient time to curethe coating, typically about 5 to 30 minutes.

In the present invention, the curing reaction is a ring-opening reactioninvolving the aminolysis of morpholine diones, and releases no volatileby-products. The aminolysis reaction of morpholine diones may bedescribed as an amide forming reaction, which still provides desirableamide crosslinks but is able to avoid significant bake-off losses. Uponcuring, the hydroxy groups may further react with the additionalcrosslinker, if present, to produce a highly crosslinked network.

The following Examples illustrate the invention. All parts andpercentages are on a weight basis unless otherwise indicated. Allmolecular weights disclosed herein are determined by GPC using apolystyrene standard. Unless otherwise specified, all chemicals andreagents were used as received from Aldrich Chemical Co., Milwaukee,Wis.

EXAMPLES

The following morpholine dione crosslinking resin solution was prepared,along with a conventional blocked polyisocyanate crosslinking resinsolution, and then principal emulsions and electrocoating compositionswere prepared therefrom and the properties of these compositions werecompared.

Example 1 Preparation of Morpholine Dione Crosslinking Resin Solution

Di-((4-butyl-2,3-dioxomorpholin-6-yl)-methyl) ether of bisphenol A wasprepared by charging about 2537 parts butylamine into a suitablereaction vessel and kept it at 0° C. under nitrogen blanket. A mixtureof about 1269 parts Epon® 828 (epoxy resin of diglycidyl ether ofbisphenol A, having an equivalent weight of 188, from Shell) and 805parts ethanol was slowly charged into the reaction vessel and kept thereaction temperature at 0° C. for 2 hours. The reaction temperature wasslowly increased to 10° C.-15° C. for 6 hours and finally to 25° C. andheld it at 25° C. until all epoxy groups were reacted as indicated by IRscan. The excess of butylamine and ethanol were removed by using rotaryevaporator. About 805 parts ethanol, 1.2 parts 4-dimethylaminopyridineand 880 parts diethyl oxalate were added into the reaction vessel andthe reaction mixture was refluxed for 2 hours under a nitrogen blanket.The excess ethanol was removed at atmospheric pressure by distillationthrough a Vigreux column and the ethanol produced upon ring closure wasremoved by heating the reaction mixture to 160° C. with a vacuum pump.The resulting resin was a brittle and colorless solid.

Example 2 Preparation of Conventional Crosslinking Resin Solution

A mixed alcohol blocked polyisocyanate crosslinking resin solution wasprepared by charging about 336.86 parts Mondur® MR (methylene diphenyldiisocyanate, from Bayer), 112.29 parts methyl isobutyl ketone and 0.07parts dibutyl tin dilaurate into a suitable reaction vessel and heatedto 82° C. under a nitrogen blanket. About 229.68 parts propylene glycolmono methyl ether was slowly charged into the reaction vessel whilemaintaining the reaction mixture below 93° C. The reaction mixture wasthen held at 110° C. until essentially all of the isocyanate was reactedas indicated by infrared scan. About 3.46 parts butanol and 73.13 partsmethyl isobutyl ketone were then added. The resulting resin solution hada nonvolatile content of 75%.

Example 3 Preparation of Chain Extended Polyepoxide Principal Emulsionwith Di-((4-butyl-2,3-dioxomorpholin-6-yl)-methyl)ether of bisphenol Aand Conventional Crosslinker

The following ingredients were charged into a suitable reaction vessel:about 520 parts Epon®828 (Epoxy resin of diglycidyl ether of bisphenol Ahaving an epoxy equivalent weight of 188, from Shell), 151 partsbisphenol A, 190 parts ethoxylated bisphenol A having a hydroxylequivalent weight of 247 (Synfac® 8009, from Milliken), 44 parts xyleneand 0.5 part dimethylbenzylamine. The resulting reaction mixture washeated to 160° C. under nitrogen blanket and held at this temperaturefor one hour. 1 part dimethylbenzylamine were added and the mixture washeld at 147° C. until an epoxy equivalent weight of 1050 was obtained.The reaction mixture was cooled to 149° C. and then 996 parts alcoholblocked polyisocyanate resin (prepared in Example 2) and 596Di-((4-butyl-2,3-dioxomorpholin-6-yl)-methyl) ether of bisphenol A resin( prepared in Example 1) were added. At 107° C., about 58 partsdiketimine (reaction product of diethylenetriamine and methyl isobutylketone at 73% nonvolatile content) and 47 parts of methylethanolaminewere added. The resulting mixture was held at 120° C. for one hour andthen dispersed in an aqueous medium of 1500 parts deionized water and 81parts methanesulfonic acid (70% methanesulfonic acid in deionizedwater). It was further diluted with 818 parts deionized water. Theemulsion was kept agitated until methyl isobutyl ketone had evaporated.The resulting emulsion had a nonvolatile content of 38%.

Example 4 Preparation of Chain Extended Polyepoxide Principal Emulsionwith Conventional Crosslinking Resin Solution

The following ingredients were charged into a suitable reaction vessel:about 520 parts Epon® 828 (Epoxy resin of diglycidyl ether of bisphenolA having an epoxy equivalent weight of 188, from Shell), 151 partsbisphenol A, 190 parts ethoxylated bisphenol A having a hydroxylequivalent weight of 247 (Synfac® 8009, from Milliken), 44 parts xyleneand 1 part dimethylbenzylamine. The resulting reaction mixture washeated to 160° C. under nitrogen blanket and held at this temperaturefor one hour. 2 parts dimethylbenzylamine were added and the mixture washeld at 147° C. until an epoxy equivalent weight of 1050 was obtained.The reaction mixture was cooled to 149° C. and then about 797 partsconventional crosslinking resin (prepared in Example 2) was added. At107° C., about 58 parts of diketimine (reaction product ofdiethylenetriamine and methyl isobutyl ketone at 73% nonvolatilecontent) and 48 parts of methylethanolamine were added. The resultingmixture was held at 120° C. for one hour and then dispersed in anaqueous medium of 1335 parts deionized water and about 81 partsmethanesulfonic acid (70% methanesulfonic acid in deionized water). Itwas further diluted with 825 parts deionized water. The emulsion waskept agitated until methyl isobutyl ketone had evaporated. The resultingemulsion had a nonvolatile content of 38%.

Example 5 Preparation of Quaternizing Agent

The quaternizing agent was prepared by adding about 87 partsdimethylethanolamine to 320 parts 2-ethyl hexanol half-capped toluenediisocyanate in the reaction vessel at room temperature. An exothermicreaction occurred and the reaction mixture was stirred for one hour at80° C. About 118 parts aqueous lactic acid solution (75% nonvolatilecontent) was then added followed by the addition of 39 parts2-butoxyethanol. The reaction mixture was held for about one hour at 65°C. with constant stirring to form the quaternizing agent.

Example 6 Preparation of Pigment Grinding Vehicle

The pigment grinding vehicle was prepared by charging about 710 partsEpon® 828 (Diglycidyl ether of bisphenol A having an epoxide equivalentweight of 188, from Shell) and 290 parts bisphenol A into a suitablevessel under nitrogen blanket and heated to 150° C.-160° C. to initiatean exothermic reaction. The exothermic reaction was continued for aboutone hour at 150° C.-160° C. The reaction mixture was then cooled to 120°C. and about 496 parts of 2-ethyl hexanol half-capped toluenediisocyanate was added. The temperature of the reaction mixture was heldat 110° C.-120° C. for one hour, followed by the addition of about 1095parts of 2-butoxyethanol, the reaction mixture was then cooled to 85°C.-90° C. and then 71 parts of deionized water was added followed by theaddition of about 496 parts quaternizing agent (prepared in Example 5).The temperature of the reaction mixture was held at 85° C.-90° C. untilan acid value of about 1 was obtained.

Example 7 Preparation of Pigment Paste

Parts by Weight Pigment grinding vehicle (prepared in Example 6) 597.29Deionized water 1140.97 Titanium dioxide pigment 835.66 Aluminumsilicate pigment 246.81 Carbon black pigment 15.27 Dibutyl tin oxide164.00 Total 3000.00

The above ingredients were mixed until homogeneous mixture was formed ina suitable mixing container. Then was dispersed by charging into Eigermill and then grinding until it pass the Hegman test.

Example 8 Preparation of Electrocoating Baths I and II

Parts by weight Bath I Bath II According to: Invention Prior ArtEmulsion (prepared in Example 3) 1503.08 — Emulsion (prepared in Example4) — 1503.08 Deionized water 2013.49 2013.49 Pigment paste (prepared inExample 7) 397.54 397.54 Conventional anti crater agent* 85.89 85.89Total 4000.00 4000.00*Conventional anti-crater agent is the reaction product of Jeffamine ®D2000 from Huntsman and Epon ® 1001 epoxy resin from Shell.

Cationic electrocoating baths I and II were prepared by mixing the aboveingredients. Each bath was then ultrafiltered. Phosphated cold rolledsteel panels were electrocoated in each bath at 240-280 volts to obtaina film 0.8-1.0 mils (20.32-25.4 μm) thick on each panel. Theelectrocoated panels were then baked at 360° F. metal temperature for 10minutes. For solvent resistance test, the electrocoated panels wereinstead baked at 330° F. metal temperature for 10 minutes.

The above prepared steel panels were tested for solvent resistance by astandard rub test (20 double rubs with a methyl ethyl ketone soaked rag)and for bake-off loss.

One method used for checking the proper cure of an e-coat film atspecified baking temperature is the solvent resistance test whichinvolves rubbing a cloth soaked in methyl ethyl ketone onto an e-coatfilm using a minimum of 20 rubs back and forth. The degree of cure canbe assessed by examining the cloth for discoloration and by examiningthe surface of the film for a dull appearance. Dull appearance on ane-coat film or discoloration on the cloth indicates poor cure of e-coatfilm.

In the above example, phosphated cold rolled steel panels coated withbath I baking at 330° F. for 10 minutes metal temperature showed no dullappearance, which indicates a complete cure. On the other hand,phosphated cold rolled steel panels coated with bath II baking at thesame temperature showed a significant amount of dull appearance orincomplete cure.

Another key factor of evaluating e-coat film is the bake-off loss duringbaking. To determine the percentage bake-off loss during baking, thefirst step is to deposit the e-coat film on pre-weighed metal panels,the residual water is removed by heating the panels at 105° C. for 3hours and finally the panels are baked at the specified time andtemperature. The percentage bake-off loss of e-coat film is determinedby the difference of the weight of e-coat before and after bakingdivided by the initial weight.

For bath I the percentage bake-off loss at 360° F. for 10 minutes metaltemperature is 8%-9% and for bath II, the percentage bake-off loss at360° F. for 10 minutes metal temperature is 12%-13%.

The results of these tests are summarized below:

Results Bath I Bath II Solvent Resistance at 330° F. 10 Min. No Rub OffDull Appearance (Good Cure) (Poor Cure) Bake Off Loss at 360° F. 10Min.* 8-9% 12-13%

The above results show that Bath I containing the morpholine dionecrosslinking agent had superior crosslinking at lower temperature andlower bake off loss that Bath II containing conventional crosslinkingagents.

1-13. (canceled)
 14. A process, comprising contacting a morpholine dionecompound with a film-forming amine compound to form a crosslinked film.15. A morpholine dione crosslinking agent having the structural formula:

wherein n is 0 or a positive integer from 1-4 and R is an alkyl grouphaving 1-8 carbon atoms, and wherein said morpholine dione is used as acrosslinking agent in a coating composition containing amine compound(s)that are capable of reacting with morpholine dione groups.
 16. Amorpholine dione crosslinking agent having the structural formula:

wherein n is 0 or a positive integer from 1-4 and R is an alkyl grouphaving 1-10 carbon atoms, and wherein said morpholine dione is used as acrosslinking agent in a coating composition containing amine compound(s)that are capable of reacting with morpholine dione groups. 17.(canceled)
 18. A substrate electrocoated with the dried and curedcomposition of claim
 1. 19. The coated substrate of claim 18, in whichthe substrate is an OEM or industrial part.
 20. The coated substrate ofclaim 19, wherein the substrate is an auto body or auto part.